Guidelines on Exposure to Electromagnetic Fields from Magnetic Resonance Clinical Systems - Safety Code 26

Preface

Magnetic resonance imaging (MRI) and recently also magnetic resonance spectroscopy (MRS) have been gaining a widespread acceptance and many applications in clinical settings. These imaging devices utilize three types of fields, namely, the static magnetic field, the time-varying magnetic field and the radio-frequency (RF) field. Since each of the fields produced by MRI or MRS devices, if of a sufficient intensity, can produce detrimental biological effects, questions have been raised regarding the safety of these devices. Guidelines on device characteristics and patient and operator exposure have been published in some countries (the United States, the United Kingdom, the Federal Republic of Germany).

This document briefly reviews biological effects of various fields used in magnetic resonance devices and provides general guidance on exposure levels to the patient and to the operator. The levels cited should not be considered as strict limits which if exceeded would result in a dangerous situation, but rather indicate the presently established levels below which potential hazards, if any, are considered minimal, if any. Higher exposure levels may still be safe, depending on various factors. For patient exposures exceeding the specified safe limits, the usual risk-benefit assessment has to be made.

This document was prepared by Dr. M.A. Stuchly, and reviewed by Mrs. D.A. Benwell, Dr. S.S. Mohanna, and Dr. M. Smith of the Bureau of Radiation and Medical Devices. Numerous valuable comments were provided by Dr. M.J. Bronskill, of Princess Margaret Hospital, Toronto, Ontario; Dr. L.D. Brown, Saskatchewan Labour, Regina, Saskatchewan; Mr. T.E. Dalgleish, Nova Scotia Department of Health, Halifax, Nova Scotia; Drs. D.J. Dorst, R.L. Nicholson and F. Prato of St. Joseph's Hospital, London, Ontario; Mr. B. Phillips, British Columbia, Ministry of Health, Vancouver, British Columbia; Dr. A.M. Sourkes, Manitoba Cancer Foundation, Winnipeg, Manitoba; Dr. R.T. Thompson, Victoria Hospital, London, Ontario; and Mr. J.M. Wetherill, Alberta Workers' Health, Safety and Compensation, Edmonton, Alberta.

Interpretation and further details of the recommendations of this safety code may be obtained from the Non-Ionizing Radiation Section, Bureau of Radiation and Medical Devices, Environmental Health Directorate, Health Protection Branch, Ottawa, Ontario, K1A 0L2.